Field emission displays have an array of hundreds of thousands of sharply pointed emitter tip electrodes, generally arranged in a plane, and an array of grid electrodes, generally arranged in a plane parallel to the plane of emitter tips. A small gap is maintained between each emitter tip and the nearest grid electrode. When a sufficient positive voltage is applied to the grid electrodes relative to the emitter tips, field emission of electrons from the emitter tips occurs, so that electrons flow from the emitter tips toward the grid. Typically, the grid is perforated so that almost all the electrons pass through the perforations and strike a cathodoluminescent coating on an anode electrode connected to a much higher positive voltage, which consequently emits light.
The emitter tips generally are organized as a matrix of pixels, with a pixel being the smallest area of the display whose illuminance is separately controlled in response to a video signal. Typically, many emitter tips are provided for each pixel to achieve adequate current flow, hence adequate display brightness.
All the emitter tips in any one pixel typically are connected together and controlled by a pixel control circuit in response to the video input signal. In an active matrix display each pixel has its own pixel control circuit. In a passive matrix display, a single pixel control circuit may control an entire row or column of pixels.
During manufacture of a field emission display, an electrical short circuit can be created inadvertently between an emitter tip and its associated grid electrode. Such short circuits may be caused by defects in the dielectric layer separating the grid from the emitter tip, or may be caused by a particulate contaminant creating a conductive bridge between the emitter tip and grid.
A single short-circuited emitter tip can render inactive (i.e., dark) the entire pixel containing the emitter tip, because the voltage across the shorted emitter tip and grid will be close to zero, thereby reducing close to zero the voltage across the remaining good electrode pairs in that pixel. As a result, the voltage across the good electrode pairs will be much too low to initiate field emission. Consequently, no current will flow through the good emitter tips, and all the current supplied by the pixel control circuit will flow through the shorted electrode pair.
Therefore, one bad emitter tip in the pixel can disable field emission from the other, good emitter tips in the pixel, causing the entire pixel to be dark.
Accordingly, there is a need to preserve the operability of a display even if one or more shorts exist between certain emitter tips and their corresponding grid or anode electrodes.